Welcome to HVAC-Talk.com, a non-DIY site and the ultimate Source for HVAC Information & Knowledge Sharing for the industry professional! Here you can join over 150,000 HVAC Professionals & enthusiasts from around the world discussing all things related to HVAC/R. You are currently viewing as a NON-REGISTERED guest which gives you limited access to view discussions

To gain full access to our forums you must register; for a free account. As a registered Guest you will be able to:

Participate in over 40 different forums and search/browse from nearly 3 million posts.

Another CVHE question

I have a chiller that I helped overhauled and have some questions. Hopefully somebody might have seen this before.

Information:
CVHE045, Serial # L00H04317

So the chiller was overhauled and a service first motor was installed. Chiller was known to have oil return problems before overhaul. All orings replaced, all flat gaskets replaced, however oil pump not not inspected or disassembled. Solenoid vent valve replaced and charge was weighed back in.

Chiller started and logged. No problems noticed. Left site and 3 weeks later customer called and said chiller went down on low differential oil pressure. Figured it might be oil filter or something simple. Installed new filter and manually turned on pump. Oil pressure was good so the chiller was started and after having run for a few minutes it tripped on differential oil pressure.

Unfortunately I was not there when the customer called and was not part of the oil pressure diagnosis but since I was there for the overhaul I am very interested in finding an answer.

All this to say, the other technician performs a variety of tests and determines that the chiller isn't making oil pressure across the journal bearing! Unit was disassembled and the journal bearing is found to be very wiped.

This time the motor is sent to a local rebuilder and is found to have shaft damage. We have had trouble in the past with service first motors and so we felt confident that we originally received a motor that was properly rebuilt. We believe after the local shop rebuilds the motor and the chiller is reassembled we should be good to go.

So now we are having a similar problem with the most recent overhaul. Upon closer investigation, it is found that the oil sump/oil is foaming each time the drive re optimizes and the chiller surges. When this happens the chiller loses most of the oil from the site glasses and the differential oil pressure drops off to about 12 psi. The surges seem more violent than the other chiller in the room which is the same setup. We set the oil trip point to 10 psi (same as the other chiller) and this has helped.

My question is why is the chiller unable to operate with the surges? Why does it lose the oil so quickly.

For what it is worth, I am an apprentice who is really curious about the reason behind problems like this and I have yet to be able to find an answer. Sorry for the long post, please ask me for any information that would help in diagnosing the problem...I may not have all the information but I have a lot.

...We set the oil trip point to 10 psi (same as the other chiller) and this has helped...

can you say: 3rd overhaul?

you need to correct this.

from what you have posted, you have not found the reason for the oil sump foaming nor have you corrected it. there is a lot to look at and can be the causes of oil foaming. not opening up the oil sump was the first issue. if you have a known oil issue, wouldn't you look into the oil sump, pump, piping system, etc. during the overhaul?

Don't step on my favorite part of the Constitution just to point out your favorite part.

Political Correctness is forced on you because you have forgotten decency.

Jayguy--I agree with what you are saying, however I am only an apprentice who was there for parts of the work and the above was a brief recollection of what I saw directly and have heard about the job. Please don't say 3rd!

R404A--What I saw was that when the machine started to surge the oil tank site glasses showed an aggressive foaming of the oil and a reduction in oil level. During this time the differential oil pressure dropped to maybe 13 or so psi. While I was there with old mechanic the machine did not trip off, even while the diff. oil alarm was set at 12 psi. I do not know what the sump pressure was at that time. As far as the lab seal...if you are referring to the oil lab seal, I remember it was around .002-.003 with the heaviest put in the 11 o'clock position.

Yes, there is an eprom installed that allows the oil heater to operate both when the chiller is off and when it is running. As I recall the oil temperature is around 130-140 degrees regardless of chiller off or on. Additionally, the motor cooling orifice size was reduced from 5/16" to roughly 9/32".

just out of curiosity why did they reduce the orfice on the cooling line?

yeah, really? i don't understand that either...with a drive, i might consider making it larger.

i understand that you are an apprentice and don't have any authority so take my comments as general in nature.

the oil pump pressure cutout setpoint is just that...a setpoint. changing it won't do anything in a normal situation. but if it allow you to run lower oil pump pressure than recommended, it is a mistake....if you are not going to follow the recommended practices of the manufacturer, why not lower it to 0 so it never trips? <-------bad idea, in case you didn't get my drift.

the chiller is going to surge with a drive...period. it is supposed to surge as it finds the surge line. after a while, it will stop and get close to the surge line but not actually surge...it will ride as close as possible to it. the oil issue is a separate deal that is not directly related to the surging but can be affected by having a drive.

Don't step on my favorite part of the Constitution just to point out your favorite part.

Political Correctness is forced on you because you have forgotten decency.

The motor cooling orifice was downsized b/c the chiller consistently ran cold and I believe use to trip off on low oil temp. This was the reasoning behind adding the eprom to allow for oil heating while running. However even after adding the eprom the chiller was still cooler than desired. Hope that make sense. Why would you want to increase it with a drive? By the way there is a flat plate heat exchanger that cools the drive.

Jayguy--Believe me I understand what you are saying. As an apprentice I ask a lot of questions and it is frustrating not being able to get answers from the older guys I work with. I don't think that anyone that I work with is too clear on what is going on with the chiller in question. I believe the idea behind adjusting the setpoints was to bring both chillers to the same point. In other words, there are 2 identical chillers in the building one which is running fine was overhauled about 1.5 years ago and then this one which was overhauled within the past couple of months. So set up both the same and then begin observing and dividing and conquering.

I understand that the drive is looking for the surge boundary, the odd thing is that this chiller seemed to hit the surge more violently and more times than the other chiller. The other chiller would hit the surge maybe twice and lightly at that. The chiller in question hit the surge 5-6 times and it sounded much worse. Anyway it was during the surge that the oil starting foaming and leaving the sump.

The vent solenoid is a Trane OEM part and it is installed in the right direction.

The is the first time I've seen a chiller of this vintage with a high mounted oil sump and a drive. I've heard many Trane drive chillers with a refrigerant pump/low mounted oil sump surge but never seen one with an oil loss/pressure problem. Why can't this chiller experience a surge or series of surges without losing oil pressure?

Thanks again for reading all of this and thanks for the comment about a good example of a post.

If the oil scavenger line coming from the evaporator (also called an eductor line) is open too far, you'll be flooding the oil sump with liquid refrigerant like R123 said, causing the oil to run cooler. When the pressures within the compressor fluctuate like they do during surge, it also causes the oil tank pressure to fluctuate. The foaming in the sump probably happens immediately after the surge when the tank pressure returns to normal, rather than during the surge.

AFD chillers need cold condenser water in order to turn down the motor, and if you have rapidly cycling tower fans and temps that fluctuate 5-8 degrees, this can also cause foaming in the sump when the entering condenser water temperature begins to drop. This is because the oil tank pressure drops, causing the liquid refrigerant to boil out of the oil.